Mercury Mariner 90hp no ignition spark help

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I am debating on buying a '83 Grumman 5.0 and it has a 90hp Mariner on it that seems to have a few problems. The owner says it fired up last year and that he replaced a switch box but I am not sure what was really done.

A little history before getting real dirty. The motor looks good. He had the cowling off all winter so there was a small amount of rust and corrosion. I pulled the plugs and they looked great! The compression on 1-5 cylinders was 152, 154, 158, 154, 154. I couldn't easily get to the bottom cylinder but after those readings I expect is okay.

Carbs probably have old fuel in them from his last attempt to start. I tested the starter solenoid and replaced it with a new one so now the starter engages the flywheel with the ignition key. I cleaned each terminal on the starter solenoid, starter and the main harness ground wires and coated them with a dielectric grease.

I measured grounds all around the engine and it seems to be good. I pulled #1 plug, grounded it and noticed no spark. I realize I probably need to check each one and I am probably jumping the gun on guessing there is a problem elsewhere (could even be the ignition or "run" switch position. Are there any quick test points to check for positive on the motor to make sure the ignition "on" is getting signal to the switch boxes?

I realize the only positive coming in is the main positive lug to the starter solenoid and from there it goes to the 20amp fuse (new, cleaned and greased) and the but rectifier but what does the gray wire from the wiring harness do since it goes to the other connector on the rectifier?

Any suggestions? Thanks!

 

[Maxz695]

Re: Mercury Mariner 90hp no ignition spark help

check for a fall overboard kill switch and if you find it make sure its engaged to fire. disconnecting the engine harness to the motor is an easier way to see if the problem lies in the key and throttle areas. The engine should get spark if the harness is disconnected from the helm hope this helps a bit

 

[accentphoto]

Re: Mercury Mariner 90hp no ignition spark help

Thats a good idea and I just ran out to try it with no spark so to see what is next. I just spend the twilight hours taking off the frame that goes around the engine to give me a more readily access to the engine. Now I can look into the carbs to see if there were any bug nests built inside. Fortunately there wasn't. Does anyone know where I should be able to measure +12v to check the incoming voltages? I have +12v at the starter solenoid, 20 amp fuse and the incoming wires to the rectifier but I am not sure how to check the stator, trigger, switch boxes or coils.

 

[CharlieB]

Re: Mercury Mariner 90hp no ignition spark help

There should NEVER be 12 volts to the switchboxes, it will kill them.

This is an AC Magneto system, the stator generates the operating voltage/current above the minimum cranking speed of 300 RPM, charging the switchboxes.

The black wire with a thin yellow line from each switchbox is the 'ground-to-kill' wire. Disconnect this wire from each switchbox, make SURE the battery, cable connections and starter are able to crank the momtor above the minimum and retest for spark. If still no spark, download the free Outboard Ignition Troubleshooting Guide available from links on the CDIElectronics website. They literally wrote the book on troubleshooting ignition problems.

A DVA meter or DVA adaptor is necessary for reliable testing, basic Ohms test are often helpful but can be misleading. Directions for building your own DVA adaptor can be found here in the forum using the search feature.

 

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Re: Mercury Mariner 90hp no ignition spark help

Thanks CharlieB. I just did some ohm measurements on the Stator and Trigger and I will post them a little later. The stator may be a little off on its ohms tolerance. The trigger seemed in the middle of the good range. I plan on building the DVA adaptor but I was not sure if it works with a DIGITAL meter. I have many digitals but no analog. Some of the meters are RMS style made by RadioShack. Now that I have the Stator and Trigger connections off (its dark outside now), I will probably put them on tomorrow and try the "ground-to-kill" wires are off of each switchbox. Is there a way to check the individual coils without having to send them power or a signal? Is there any simple ohms test or is this inaccurate? Now to see if there are any instructions out there on how to test the switchpacks while the wires are off of them and they are not powered. I almost forgot, how is the rectifier tested?

 

[accentphoto]

Re: Mercury Mariner 90hp no ignition spark help

Here is a quote from a earlier forum with specs and my actuals beside it:

Here is the test for the Stator. Make sure that the wire are disconnected that come from the stator going to the switch boxes and rectifier.

Using the Rx 1000 scale take a reading between the BLUE and RED stater wires = 5400 - 6200 Ohms - I read 4980 Ohms

Using Rx1000 scale take a reading between the BLUE/WHITE and RED/WHITE stator wires = 5400 - 6200 Ohms - I read 6600 Ohms

Using the Rx1 scale take meter reading between the RED stator and engine ground = 125 Ohms - 175 Ohms - I read 146.4 Ohms

Using Rx1 scale take a reading between RED/WHITE stater wire and engine ground = 125 Ohms - 175 Ohms - I read 146.4 Ohms

If any of you readings are less or more than stated, Replace Stator!


Trigger Test

Make sure all wires are disconnected from Trigger to Switchboxes!

Using the Rx100 scale

Test between the BROWN Trigger wire W/O yellow sleeve and WHITE Trigger wire WITH yellow sleeve = 1100 Ohms - 1400 Ohms - I read 1228 Ohms

Test between WHITE Trigger wire W/O yellow sleeve and VIOLET trigger wire WITH yellow sleeve = 1100 Ohms - 1400 Ohms - I read 1246 Ohms

Test between VIOLET Trigger wire W/O yellow sleeve and BROWN Trigger wire WITH yellow sleeve = 1100 Ohms - 1400 Ohms - I read 1247 Ohms

If an of your reading are less or more than stated, Replace Trigger.

So I guess my Stator is bad??? and my Trigger is good??? I did notice the trigger seems to have newer looking thinner wires and the stator has thicker, deteriorating thicker wires.

Also, the PO mentioned he had some electrical repair done and from what I could tell it looked like only ONE switchbox had been replaced!

This is going to hurt if I need to replace two switchboxes and a stator. Who knows, the rectifier and some coils may be bad too.